Question

Does anyone know of an editor that has the ability to enforce exact line lengths (bonus if it allows association of maximum line lengths by file name/extension)?

What I mean by exact line lengths is that the editor will always save each line padded to a maximum line length (defined by the user). For example, if a file should have a 120-character line length every line in the file will be 120-characters long, padded with blanks if needed, follow by the appropriate newline indicator. When someone edits a line the editor will prevent them from typing if the line length hits the max length.

Platform is Win XP/Vista.

Answer 1

Vim

:syn match Error /^.{,119}$/
:syn match Error /.{121,}/

This will cause any lines of length != 120 to be highlighted with a solid red background (in the default color scheme).

If you write this (without the leading colons) into $VIMRUNTIME/syntax/foo.vim, and place

:au BufRead,BufNewFile *.foo    set filetype=foo
:au Syntax foo  source $VIMRUNTIME/syntax/foo.vim

in vimrc or the usual ftdetect and synload.vim locations, then as long as syntax highlighting is enabled, these rules will will automatically apply to any *.foo file you open in Vim.

(See :h mysyntaxfile-add if you want to add to an existing syntax file, and see :h rtp for the default $VIMRUNTIME path on your platform.)